Magnetic Disk Apparatus and Method

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-081566, filed on May 20, 2024; the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a magnetic disk apparatus and a method.

Conventionally, repeatable run-out (RRO) has been known as one of factors of a positioning error of a magnetic head in a magnetic disk apparatus. RRO refers to a positional deviation between a track trajectory defined by a burst pattern and an actual track trajectory. RRO fluctuates in synchronization with the rotation of the magnetic disk (and a spindle motor).

In a manufacturing process of the magnetic disk apparatus, a correction value (hereinafter, referred to as an RRO correction value) for correcting the positional deviation due to the RRO at a plurality of radial positions is measured. The measured RRO correction value is stored in a nonvolatile storage area as additional information of servo data. When the magnetic disk apparatus is operated, a position of the magnetic head is corrected by using the RRO correction value.

According to the present embodiment, a magnetic disk apparatus includes a magnetic disk, a magnetic head, and a controller. On the magnetic disk, multiple first positions are set in a radial direction and multiple tracks are provided. The multiple first positions are positions at which repeatable run-out (RRO) correction values are measured. The multiple first positions include multiple second positions and a third position different from the multiple second positions. The magnetic head includes a write head that is configured to perform write access to the magnetic disk, and a read head that is configured to perform read access to the magnetic disk. The controller is configured to execute a first process in which an RRO correction value is measured at each of the multiple second positions and measurement of an RRO correction value at the third position is skipped. The measuring of the RRO correction value at each of the multiple second positions includes, for each second position, moving the magnetic head to place the read head at a fourth position being one of the multiple second positions, acquiring a first position error signal by the read head while keeping the read head at the fourth position, and calculating an RRO correction value at the fourth position based on the first position error signal. The controller is configured to execute, after the first process, a second process of performing the write access or the read access to the multiple tracks. The second process includes acquiring a second position error signal by the read head during the write access or the read access, and calculating an RRO correction value at the third position based on the second position error signal.

Hereinafter, the magnetic disk apparatus and a method according to embodiments will be described in detail with reference to the attached drawings. Note that the present invention is not limited to the embodiments.

is a diagram illustrating an example of a configuration of a magnetic disk apparatusof an embodiment.

The magnetic disk apparatusis connected to a host. The magnetic disk apparatuscan receive an access command such as a write command or a read command from the host.

The magnetic disk apparatusincludes a magnetic diskhaving a magnetic layer formed on its surface. The magnetic disk apparatusaccesses the magnetic diskin response to the access command. The access includes write of data and read of data.

The write of data and the read of data are performed through a magnetic head. Specifically, the magnetic disk apparatusincludes a spindle motor (SPM), a ramp, an actuator arm, a voice coil motor (VCM), a servo controller (SVC), the magnetic head, a hard disk controller (HDC), a preamplifier, a read/write channel (RWC), a processor, a flash read only memory (FROM), and a dynamic random access memory (DRAM), in addition to the magnetic disk.

The magnetic diskis rotated at a predetermined rotational speed by the SPMthat is coaxially attached.

The SVCis an integrated circuit serves as a driver that drives the SPMand the VCM. The processorcontrols the rotation of the SPMand the rotation of the VCMvia the SVC.

The magnetic headincludes a write headand a read head. The magnetic headwrites data to the magnetic diskthrough the write head. The magnetic headreads data from the magnetic diskthrough the read head. The magnetic headis attached to a distal end of the actuator arm. The magnetic headis moved in the radial direction of the magnetic diskby the VCMthat is driven by the SVC. Note that one or both of the write headand the read headincluded in the magnetic headmay be plurally provided in a single magnetic head.

When the rotation of the magnetic diskis stopped, the magnetic headis moved onto the ramp. The rampis configured to hold the magnetic headat a position separated from the magnetic disk.

The preamplifieris an integrated circuit that performs write and read of data through the magnetic head. During a read operation, the preamplifieramplifies a signal read by the magnetic headfrom the magnetic diskand outputs the amplified signal to be supplied to the RWC. During a write operation, the preamplifieramplifies a signal corresponding to write target data supplied from the RWCand supplies the amplified signal to the magnetic head.

The HDCcontrols transmission and reception of data to and from the hostvia an I/F bus, and controls the DRAM.

The DRAMis used as a buffer of data to be transmitted to and received from the host. In one example, the DRAMis used for temporarily storing data to be written or data read from the magnetic disk.

In addition, the DRAMis used as operation memory by the processor. The DRAMis used as an area in which a firmware program is loaded and an area in which various types of management data are temporarily stored.

The RWCmodulates write target data supplied from the HDCand supplies the modulated data to the preamplifier. In addition, the RWCexecutes demodulation including error correction on a signal, which has been read from the magnetic diskand supplied from the preamplifier, and then outputs the signal to the HDCas digital data.

The processoris, for example, a central processing unit (CPU). The flash read only memory (FROM)and the DRAMare connected to the processor.

The FROMstores the firmware program, various types of setting information, and the like. Note that the firmware program may be stored in the magnetic disk.

In addition, the processorperforms overall control of the magnetic disk apparatusin accordance with the firmware program stored in the FROMor the magnetic disk. For example, the processorloads the firmware program from the FROMor the magnetic diskinto the DRAM, and executes control of the SVC, the preamplifier, the RWC, the HDC, and the like in accordance with the firmware program loaded into the DRAM.

Note that some or all of functions of the processormay be implemented by a hardware circuit such as a field-programmable gate array (FPGA) and an application specific integrated circuit (ASIC).

The HDC, the RWC, and the processorare configured as a system-on-a-chip (SoC)that is one integrated circuit. In addition to these devices, the SoCmay include other elements (for example, the FROM, the DRAM, or the like). Note that the SoCis an example of a controller.

is a view illustrating an example of a configuration of the magnetic diskin the embodiment. Note that this drawing illustrates an example of a rotational direction of the magnetic disk. The magnetic headmoves relative to the magnetic diskby the rotation of the magnetic disk. Therefore, a write/read direction, namely, a direction in which data is written or read by the magnetic headin the circumferential direction is opposite to the rotational direction of the magnetic disk.

In the radial direction, a direction from a rim to a center of the magnetic diskis referred to as an inner diameter (ID) direction, and a direction from the center to the rim of the magnetic diskis referred to as an outer diameter (OD) direction.

Servo data used for positioning of the magnetic headis written to the magnetic diskby, for example, a servo writer or self-servo write (SSW) in a manufacturing process. According to, servo areas SV that are arranged radially in the radial direction and at predetermined intervals in the circumferential direction are provided, as an example of arrangement of servo areas in which the servo data is written. A data area DA in which data is written is provided between two servo areas SV adjacent to each other in the circumferential direction.

A plurality of concentric servo tracksis provided in the radial direction of the magnetic disk. The servo data written in the servo area SV is used for positioning of the magnetic head.

More specifically, the concentric data tracks are provided above an area of the magnetic diskwhere the servo tracksare provided. The servo tracksmay be used as the data tracks, or the data tracks different from the servo tracksmay be provided. A plurality of data sectors is arrayed in the circumferential direction in an area divided by the data area DA on each data track. Data may be written to each data sector by the magnetic head. Note that data that may be written to each data sector includes user data received from the host, metadata (for example, error correction code) accompanying the user data, system data, and the like. The magnetic disk apparatusholds, in advance, the setting of the positional relationship between the servo tracksand the data tracks. The magnetic disk apparatusexecutes positioning control for positioning the magnetic headin a target data track based on the servo data recorded in the servo area SV. The positioning control includes a seek operation that is an operation of moving the magnetic headin the radial direction toward the target data track, a tracking operation of keeping the magnetic headon the target data track, and the like.

Note that the data tracks are an example of the multiple tracks.

The servo data includes sector/cylinder information, a burst pattern, an RRO correction value, and the like. The sector/cylinder information indicates a servo address (servo sector address) in the circumferential direction of the magnetic diskand a position (track number) of a track set in the radial direction. The track number obtained from the sector/cylinder information is an integer value, and the burst pattern represents an offset amount after the decimal point with the track number as a reference.

An ideal shape of the track is a perfect circle. However, the servo trackis warped due to vibration or the like occurring when the servo data is written. Thus, there is a case where a position in the radial direction (radial position) that is specified based on the burst pattern (more precisely, a combination of the sector/cylinder information and the burst pattern) deviates from an ideal radial position. This positional deviation causes deterioration in positioning accuracy. This positional deviation occurs repeatedly in the same manner with one rotation of the magnetic disk (and the spindle motor) as a cycle, and thus, is called RRO. In the manufacturing process, the RRO correction value is learned at a plurality of radial positions. In use of the magnetic disk apparatus, when performing positioning of the magnetic headon the target track, control to cancel the positional deviation caused by RRO is executed based on the RRO correction values.

Note that a place where each of the RRO correction values obtained at the radial positions is stored is not necessarily the servo area SV as long as the place is a nonvolatile storage area. Each of the RRO correction values may be stored in the data area DA or may be stored in a nonvolatile memory such as the FROM. In the magnetic disk apparatus, the RRO correction value is read from the nonvolatile storage area, and the position of the magnetic headis corrected by using the read RRO correction value.

Hereinafter, a process of measuring the RRO correction values at the plurality of radial positions is referred to as an RRO learning process. In addition, each of the radial positions where the RRO correction value is measured is described as a measurement position or an RRO measurement position. The correction of the positional deviation by RRO is referred to as RRO correction.

Measurement positions may be set independently of the arrangement of a group of the data tracks. In a case where a target data track exists at a radial position between two measurement positions adjacent to each other, the SoCexecutes the RRO correction as follows. The SoCestimates an RRO correction value at the radial position of the target data track by interpolation of RRO correction values including RRO correction values of the two measurement positions. The SoCthen executes the RRO correction by using the RRO correction value obtained by the estimation.

The interpolation may be linear interpolation using the respective RRO correction values of the two measurement positions adjacent to the target data track. Alternatively, the interpolation may be second or higher order polynomial interpolation using RRO correction values of three or more measurement positions including the two measurement positions.

Measurement positions are set at as fine intervals as possible in the radial direction in order to enhance the positioning accuracy as much as possible. Measurement of an RRO correction value at one measurement position includes measurement of a position error signal at the one measurement position and calculation of the RRO correction value based on the measured position error signal. Since a large number of measurement positions are set and RRO correction values at all the measurement positions are measured, the RRO learning process requires a large amount of time.

In the embodiment, the SoCis configured to skip the measurement of RRO correction values at some measurement positions in the RRO learning process in order to reduce the time required to measure the RRO correction values at all the measurement positions.

The manufacturing process includes a process of writing data to all the data tracks of the magnetic diskor reading data from all the data tracks of the magnetic diskafter the RRO learning process. An operation of writing data to all the data tracks of the magnetic diskis referred to as a write-all process. An operation of reading data from all the data tracks of the magnetic diskis referred to as a read-all process. A pair of the write-all process and the read-all process is executed to detect a defective data sector and verify whether each data sector can be normally accessed. The pair of the write-all process and the read-all process may be executed multiple times. The manufacturing process may include a defective data sector detection process and a defect servo sector detection process other than the write-all process and the read-all process.

The multiple measurement positions may include a radial position that is accessed in the write-all process or the read-all process. Such a radial position accessed in the write-all process or the read-all process among the multiple measurement positions is referred to as a specific measurement position. In a case where the multiple measurement positions includes a radial position accessed in the defective data sector detection process or the defective servo sector detection process, the radial position may be used as the specific measurement position.

In the RRO learning process, the SoCskips measurement of an RRO correction value at the specific measurement position. When accessing the specific measurement position or the vicinity of the specific measurement position in the write-all process or the read-all process after the RRO learning process, the SoCmeasures an RRO correction value at the specific measurement position. Thus, in the RRO learning process, the seek operation of the magnetic headand the tracking operation for one cycle of the data track are omitted for each specific measurement position, and the time required for measuring the RRO correction values at all the measurement positions is shortened. Thus, the efficiency of the RRO correction value measurement is improved.

Prior to description as to details of the multiple measurement positions and the specific measurement position, a radial position where the read headpasses over and a radial position where the write headpasses over will be described.

is a view for describing an example of the positional relationship between the read headand the write headin the embodiment. According to the example illustrated in this drawing, the read headand the write headare arrayed in an extending direction of the actuator arm. The read headis arranged on a side closer to a rotation axis of the actuator armthan the write head

In the example illustrated in, in a case where the read headis positioned on a given data track, an angle θ, formed by an array direction of the read headand the write headand a tangential direction of the track as a positioning target is non-zero. As a result, a radial position of the read headand a radial position of the write headare different. When a distance from a rotation center C of the magnetic diskto the radial position of the read headis expressed as rr and a distance from the rotation center C of the magnetic diskto the radial position of the write headis expressed as rw, the radial position of the read headand the radial position of the write headare separated by L (=|r-r|) in the radial direction of the magnetic disk. Hereinafter, L is referred to as a distance between head positions.

The distance between head positions may vary with a position of the magnetic head.is a view for describing that the distance between head positions varies with the position of the magnetic headin the embodiment.

At a position P, a direction in which the write headand the read headare arranged is orthogonal to the radial direction. In such a case, the radial position of the read headand the radial position of the write headbecome equal, so that the distance between head positions L is zero.

In a case where the magnetic headis in an area Aon the inner peripheral side of the position P, for example, in a case where the magnetic headis placed at a position P, the write headis located on the inner peripheral side of the read headas in the example illustrated in. In short, the distance between head positions L is non-zero. A value of the distance between head positions L increases as the position of the magnetic headmoves away from the position Pto the inner peripheral side.

In a case where the magnetic headis in an area Aon the outer peripheral side of the position P, for example, in a case where the magnetic headis placed at a position P, the write headis located closer to the outer peripheral side of the magnetic diskthan the read head. In short, the distance between head positions L is non-zero. A value of the distance between head positions L increases as the position of the magnetic headmoves away from the position Pto the outer peripheral side.

Note that the examples illustrated inare merely examples. For example, the arrangement direction of the write headand the read headdoes not necessarily coincide with the extending direction of the actuator arm.

is a view for describing the multiple measurement positions and the specific measurement position in the embodiment. This drawing illustrates a partial area included in the area Aon a recording surface of the magnetic disk. Thus, the write headis located closer to the outer peripheral side of the magnetic diskthan the read head